The present invention generally relates to fuel injectors, and more particularly high pressure gaseous fuel injectors for internal combustion engines.
The natural gas transmission industry and chemical process industries use a large number of large-bore, 2-stroke and 4-stroke natural gas engines for compressing natural gas. For example, industries use these engines for such purposes as maintaining pressure in the extensive network of natural gas pipelines that supply residential housing and commercial businesses. The network of natural gas pipelines typically operate at high pressures in the neighborhood of between 500 psig and 1000 psig.
These large-bore, natural gas engines may be powered by a small portion of the natural gas passing through the pipelines. However, before being injected into the engine, the pressure of the gas is significantly and substantially reduced. Gaseous fuel is typically injected into these cylinders at low pressures (for example, 15 psig to 60 psig by mechanically actuated fuel injectors, such as that disclosed in Fisher, U.S. Pat. No. 4,365,756. The problem with low pressure injection is that the fuel pressure provides little kinetic energy with which to induce cylinder charge mixing. There is ample evidence that the fuel and air in these large bore engines are not well mixed and as such exhibit poor combustion stability, high misfire rates and significant cycle-to-cycle variations in peak pressure. As a result, these engines are not efficient and also are environmentally detrimental, contributing to approximately 10% of the total NOx production in the United States from stationary combustion sources according to estimates.
The concept of using high pressure fuel delivery to enhance fuel mixing in these engines has been proposed as a means to improve efficiency and environmental emissions from these engines. However, retrofitting existing engines provides a significant hurdle because these engines are manufactured by different companies and also vary in size. Moreover, injecting fuel at high pressure as opposed to low pressure requires the fuel injectors to operate under extremely high operating pressures which in turn greatly increases stresses and powering requirements for opening and closing the valves. A key requirement for any proposed high pressure fuel injector is reliability. These large-bore, natural gas engines typically run continuously over long time periods, meaning that any suitable fuel injector must be capable of reliably enduring very long operating cycles of the engine. It is desirable for example, that the fuel injectors reliably operate over several hundred million continuous cycles of the engine (about one to two years before replacement). As such, a valve must achieve reliability over this long time period or operating interval. Fuel injectors of the prior art such as that disclosed in Fisher, U.S. Pat. No. 4,365,756 are not capable of reliably sealing and accurately controlling the injection of gas at high pressure. Only recently have economic and environmental pressures on the gas industry resulted in justification for advances in fuel injection technology. For at least the foregoing reasons, commercial large bore 2-stroke and 4-stroke natural gas engines continue to be fueled at low pressure by conventional low pressure fuel injectors.
It is the general aim of the present invention to provide a commercially reliable and practical fuel injector for injecting high pressure gaseous fuel (eg. around 300-700 psi or more) into combustion engines.
It is an object of the present invention according to one aspect to provide a fuel injector that can withstand the forces of high pressure gaseous fuel and has a long service operation but does not leak either gaseous fuel or hydraulic fluid to the external environment.
It is another object of the present invention according to another aspect to provide a fuel injector that is universal in that the fuel injector assembly can be easily adapted without any or any substantial redesign to fit and operate as desired on the various types and sizes of combustion engines in industry.
It is a another object of the present invention according to another aspect to provide a highly reliable fuel injector, and specifically one that is not susceptible to thermal damage from the engine.
It is another object to provide a fuel injector with increased operating life, whereby gas leakage, eventually expected from o-rings and sliding gas seals, is captured and safely and properly disposed of, on an ongoing basis, not requiring engine shut-down to replace the injector valve.
In accordance with these and other aims and objectives, the present invention is directed towards a novel fuel injector cartridge, a novel fuel injector that includes a tubular cartridge housing and the fuel injector cartridge inserted therein, and an electrohydraulic fuel injector assembly incorporating the fuel injector and an electrohydraulic valve, all for facilitating the injection of high pressure gaseous fuel. According to the present invention, the fuel injector is operated by hydraulic oil to successively open and close to inject gas into the cylinders of the engine in sequence with the engine cycles. The invention includes at least one oil collection chamber for collecting leakage of hydraulic oil and/or any gas for safe removal.
According to the preferred embodiment, two interconnected chambers are provided. One chamber collects oil leakage past the piston and gas leakage past the gas valve. The second chamber collects any other leakage between the electrohydraulic valve and the fuel injector. Gas seal leakage is not anticipated for new fuel injectors and their cartridges, but it will be appreciated that over the course of several hundred million operating cycles, wear of gas seals can occur, and particularly, the gas valve seal engaging the moving valve, and as such, gas leakage can occur. The collected oil and/or gas is directed through a separate outlet port away from the entire assembly to a remote gas and oil separator to remove gas from the oil and recycle the oil. A small clearance may be provided between the piston and the piston chamber or bore in which it reciprocates to regulate and limit the amount of leakage and thereby provide a controlled amount of leakage.
Several advantages may result from the availability of leaked oil in the fuel injector assembly. One advantage is that the leaked oil can be used to lubricate the contact surfaces between an upper guide and the valve. This allows for a precision hardened steel upper guide without wear concerns that provides accurate guiding of the gas valve, prolonging the life of the gas valve seat and sliding dynamic gas valve seal. Another advantage is that the collection chambers and associated passages provide a low pressure buffer between the high pressure gaseous fuel and high pressure hydraulic operating fluid, as well as between these high pressure locations inside the fuel injector and the external atmosphere.
In the preferred embodiment, two collection chambers are provided, one between the electrohydraulic valve and the fuel injector cartridge, and one between the valve and piston inside of the cartridge. The novel fuel injector cartridge of the present invention may be replaced periodically, typically more frequent than other components of the system. The structure of the preferred embodiment provides a cost effective means for periodically replacing the fuel injector cartridge.